Thus, this method of analysing wave measurements
yields a distribution of the energy of the various
wave components, E(f,θ). It was noted in Section 1.3.2
that wave energy travels at the group velocity cg, and
from Equation 1.15 we see that this is a function of
both frequency and direction (or the wavenumber
vector) and possibly water depth. The energy in each
spectral component therefore propagates at the associated
group velocity. Hence it is possible to deduce how
wave energy in the local wave field disperses across the
ocean.